The U.S. vs. IRAN: Why we've been in conflict for 40 years and where we go from here.

• Author: Smith, Patricia
• Position: INTERNATIONAL

Last month, when the U.S. killed Iran's top general, tensions between these longtime foes soared, and the two countries came as close to outright war as they have in their four-decade-long conflict.

Major General Oassim Suleimani (right), who led Iran's elite Quds force of the Revolutionary Guard, was killed by an American drone that fired missiles into his convoy as it was leaving the airport in Baghdad, the Iraqi capital. As the architect of Iran's military operations across the Middle East, Suleimani was responsible for the deaths of hundreds of Americans since the war in Iraq began in 2003. He was also close to Iran's Supreme Leader, Ayatollah Ali Khamenei, and widely considered to be the second most powerful man in Iran.

The killing came after more than a year of rising tensions between Iran and the U.S. In 2018, President Trump pulled the U.S. out of the 2015 Iran nuclear deal, which was designed to halt Iran's nuclear weapons program in exchange for lifting economic sanctions that had crippled Iran's economy. Since pulling out of the agreement, the U.S. has imposed even tougher sanctions on Iran, and Iran has responded with a series of increasingly provocative actions.

Here's what you need to know to understand how this latest crisis fits into the long history of conflict between the two countries and what the flare-up might mean for the future.

1. What sparked the most recent conflict?

   The crisis began in December, when Iranian-backed militia groups fired a rocket into an Iraqi military base outside Kirkuk, killing an American contractor working there. In retaliation, the U.S. attacked five Iranian-backed militia groups--three in Iraq and two in Syria--in which about two dozen fighters were killed and many more wounded.

   Because of that death toll, many Iranians and Iraqis viewed those strikes as out of proportion to the attack on the Iraqi base. Their outrage sparked large-scale demonstrations in Baghdad. The protesters, who were largely members of Iranian-backed militias, stormed the American embassy; they succeeded in breaching the compound's outer walls and set fire to a reception building.

   After the embassy attack, the U.S. killed Suleimani on Hump's order. The U.S. says it was acting in self-defense.

   "In recent days, he was planning new attacks on American targets," Trump said. "But we stopped him."

   Almost everyone agrees that Suleimani had American blood on his hands. But there's considerable disagreement about the justification for and the wisdom of killing a high-ranking Iranian leader.

   "From Iran's perspective, it is hard to imagine a more deliberately provocative act," says Robert Malley of the International Crisis Group.

2. Why have the U.S. and Iran been at odds for...